Polyester film roll

ABSTRACT

A polyester film roll is rolled on a core, wherein the difference R (m) between the maximum value and the minimum value of the diameters of the roll is not more than 2W×10 −3  and not more than L×10 −7 , when the diameters of said roll are measured in the width direction of the roll, (therein, W is the width (m) of the film roll, and L is the length (m) of the rolled film). Alternatively, among the lengths of lines which are obtained by measuring the diameters of said roll in the width direction of the roll, drawing a straight line between both the ends of the curved line of the obtained roll diameters, the maximum distance on the convex portion between the curved and straight lines is not more than 500 μm, and the maximum distance on the concave portion of the same is not more than 300 μm.

TECHNICAL FIELD

The present invention relates to a polyester film roll, in more detail,to a polyester film roll which is free from the generation of wrinkleson the film and has a good roll appearance.

BACKGROUND ART

The polyester films have excellent in strengths, dimensional stability,and so on, and have widely been used for magnetic recording media,capacitors, packages and printing materials. Video tapes, audio tapes,computer tapes, and soon, are widely known as the magnetic recordingmedia using the polyester films as supports (base films).

High density recordings on the magnetic recording media are progressedin recent years, accompanied by the formation of thin and flat basefilms. However, it is difficult to roll a thin flat film in a roll-likeshape in a good rolled appearance. Even when the thickness of a film isslightly uneven, the unevenness of the film is accumulated, when rolledin the roll-like shape. Consequently, the thin portion of film isdeformed into a wrinkle-like shape, and the thick portion of the film isextended and forms slacks, when the film is unrolled, whereby troublesare caused when the film is subjected to a processing such as a coatingprocessing or a vacuum-deposition processing.

In order to solve the problems, various techniques such as theimprovement in the surface characteristics of a film [JP-A 59-95116(hereafter, JP-A means Japanese unexamined patent publication), JP-A59-171623, JP-A 2-194924, JP-A 3-207727, and so on], the reduction ofthickness unevenness (JP-A 48-43772, JP-A 52-47070, JP-A 54-56674, JP-A1-95025, JP-A 1-295822, and so on), or the dispersion of the thicknessunevenness into the width direction by oscillation (JP-A 36-22875, JP-A39-14534, and so on] have been proposed.

DISCLOSURE OF THE INVENTION

However, the conventional techniques had problems such as a problem inwhich the characteristics of the film have to be changed, a problem inwhich wrinkles or slacks are generated with the passage of time, evenwhen the film does not have a problem in a rolled state, and a problemin which a technique can not be applied to a practical production,because the development of the technique is extremely difficult.Especially, such the problems have been actualized, when the films arethinned and flattened.

The purposes of the present invention is to improve the problems, and toprovide a polyester film roll which does not change the characteristicsof the film, is free from the generation of wrinkles and slacks whichare generated with the passage of time, and has a good roll appearance.

According to the present invention, the above-described purposes andadvantages of the present invention are achieved, firstly, by apolyester film roll (hereinafter often referred to as the firstpolyester film roll) in which a polyester film is rolled on a core,characterized in that the difference R (m) between the maximum value andthe minimum value is not more than 2W×10⁻³ and not more than L×10⁻⁷,when the diameters of said roll are measured in the width direction ofthe roll. Therein, W is the width (m) of the film roll, and L is thelength (m) of the rolled film.

According to the present invention, the above-described purposes andadvantages of the present invention are achieved, secondly, by apolyester film roll (hereinafter often referred to as the secondpolyester film roll) in which a polyester film is rolled on a core,characterized in that, among the lengths of lines which are obtained bymeasuring the diameters of said roll in the width direction of the roll,drawing a straight line between both the ends of the curved line of theobtained roll diameters, and then vertically drawing the lines from saidcurved line to said straight line, the maximum length (maximum convexportion) on the convex portion side from said straight line is not morethan 500 μm, and the maximum length (maximum concave portion) on theconcave portion side from said straight line is not more than 300 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the method of measuring roll diameters in the widthdirection of the film roll. FIG. 1B shows the diameters of the filmroll/distance from the edge of film roll in the width direction.

FIG. 2 is a diagram showing the difference R between the maximumdiameter value of the film roll and the minimum diameter value of thefilm roll. W is the width of the film roll, and L is the rolled lengthof the film roll.

FIG. 3 is a diagram showing a curved line with two ends corresponding toall the diameters of the film roll along the width direction of theroll, a straight line connecting the two ends of the curved line, afirst perpendicular line (with respect to the straight line)intersecting the straight line and the maximum convex area of the curveline, and a second perpendicular line (with respect to the straightline) intersecting the straight line and the maximum concave area of thecurve line.

FIG. 4 shows the measurement of all the diameters of the film roll alongthe width direction of the roll.

FIG. 5 shows an image of the shape of the film roll.

FIG. 6 shows the definitions of the shape of the film roll in terms ofthe image shown in FIG. 5.

EMBODIMENT OF THE INVENTION

Hereinafter, the first polyester film roll of the present invention willbe explained.

The polyester film in the present invention may be an unoriented film ora monoaxially oriented film, but is preferably a biaxially oriented filmespecially oriented in the longitudinal direction (machine direction)and in the width direction (transverse direction).

The polyester film includes films comprising aromatic polyesters(homopolymers) represented by polyethyelene terephthalate, polyethylene2,6-naphthalenedicarboxylate, and polybutylene terephthalate, or thefilms of these copolymers. Among the polymers, the polyethyleneterephthalate and the polyethylene 2,6-naphthalenedicarboxylate arepreferable from the viewpoint of uniform film-forming properties.

The polyester film may be a mono-layered film or a laminate filmcomprising two or more layers, and may be a balanced film whosemechanical properties are approximately equal in two axial directions ora reinforced film which is reinforced in one axial direction.

The polyester film may contain inner deposited particles deposited onthe polymerization of the polyester, and inactive particles added beforethe formation of the film, such as inactive inorganic particlesrepresented by calcium carbonate particles, alumina particles, sphericalsilica particles, and titanium oxide particles, and organic particlesrepresented by cross-linked silicone resin particles, cross-linkedpolystyrene resin particles, cross-linked acrylic resin particles,cross-linked polyester resin particles, cross-linked styrene-acrylicresin particles, polyimide particles, melamine resin particles.

The average particle diameter of these inactive particles is preferablynot less than 0.01 μm and not more than 2.0 μm. The lower limit of theaverage particle diameter is further preferably 0.05 μm, furthermorepreferably 0.1 μm, while the upper limit is further preferably 1.0 μm,furthermore preferably 0.7 μm. The content of the inactive particles ispreferably not less than not less than 0.001 percent by weight and notmore than 2.0 percent by weight. The lower limit of the content isfurther preferably 0.005 percent by weight, furthermore preferably 0.01percent by weight, while the upper limit is further preferably 1.0percent by weight, furthermore 0.5 percent by weight.

The polyester film roll in the present invention is the film roll whichthe polyester film is rolled on the core, and needs that the differenceR (m) between the maximum value and the minimum value is not more than2W×10⁻³ and not more than L×10⁻⁷, when the diameters of said roll aremeasured in the width direction of the roll. Preferably, R (m) ispreferably not more than 1.5W×10⁻³ and not more than (L/1.5)×10⁻⁷.Therein, W is the width (m) of the film roll, and L is the length (m) ofthe rolled film.

In the case of not satisfying the above-described equations, thepolyester film roll is not preferable, because the accumulated thicknessunevenness of the roll shape is enlarged, thereby easily generatingwrinkles on the roll in the thin portion of the film and easilyextending the thick portion to generate slack on the film, when the filmis unrolled from the roll. Even when the polyester film roll does nothave a local uneven portion in the profile of the roll shape but whenthe whole shape of the polyester film roll is obliquely inclined, thepolyester film roll is also not preferable, because one side (on thelarger outer diameter side of the roll) of the film is slackened on theunrolling of the film from the roll and because the rolling of the filmis shifted on the rolling of the film in the next process, althoughwrinkles are scarcely generated.

A method for producing the above-described polyester film roll isespecially not limited, but preferably includes a method comprisingmeasuring the thickness of the continuously produced and traveling filmin high accuracy or measuring the roll shape values (outer diameters) ofthe rolled film roll in the width direction, and then feeding back themeasured values to adjust the temperature and gap of die lips so as tosatisfy the shape of the roll of the present invention, thus adjustingthe thickness of the film. The former high accuracy measurement methodis the most ideal method, because of enabling the control in highresponse, but the latter method can be combined with a conventionalthickness unevenness-adjusting method and also has advantages that theaccuracy shortage of said method is covered and that an increase in thecost is restrained. In the former method for measuring the thickness ofthe traveling film, a non-contact type hardness meter generally usedonline, such as a transmitted β-ray attenuation method thickness meter,a transmitted infrared light attenuation method thickness meter, or anoptical interferencial spectoscopy thickness meter, is used. In thelatter roll shape method, a stylus type thickness meter, a non-contactlaser type thickness meter, or the like, is also used.

The degree of rolling hardness of the polyester film roll in the presentinvention is preferably not less than 90 and not more than 100, furtherpreferably not less than 95 and not more than 100. When the degree ofrolling hardness is less than 90, the polyester film roll tends togenerate wrinkles with the passage of time, and is further liable tocause the slippage of the rolled film.

The width and length of the polyester film in the present invention areespecially not limited, but are generally 0.300 to 1.500 m and 3,000 to30,000 m, respectively, from the viewpoint of productivity in anindustrial scale. The effects of the present invention especiallyremarkably appear on the roll of a film having a width of not less than0.400 m and a length of not less than 5,000 m. The thickness of the filmis preferably not less than 0.5 μm and not more than 20 μm, furtherpreferably not less than 3 μm and not more than 10 μm. A film having athickness of less than 0.5 μm is inferior in a rolling property becausethe rigidity of the film is extremely low, while a film having athickness of more than 20 μm has high rigidity, therefore they scarcelyexpress the effects of the present invention.

The surface roughness Ra of the polyester film in the present inventionis preferably not less than 0.1 nm and not more than 10 nm, furtherpreferably not less than 0.3 nm and not more than 8 nm, especiallypreferably not less than 0.3 nm and not more than 5 nm. When the Ra ofthe polyester film is less than 0.1 nm, the polyester film is notpreferable, because the polyester film has an inferior slipping propertyand gives only film rolls having extremely inferior rolled appearances.On the other hand, a coarse polyester film having a Ra of more than 10nm hardly becomes the target of the present invention, because thepolyester film scarcely generates wrinkles, even when the shape of theroll does not satisfy the conditions of the present invention.

The outer diameter of the roll-shaped core of the polyester film roll inthe present invention is especially not limited, but is usually 0.100 to0.400 m. When the outer diameters of the roll shape of the core aremeasured in the width direction of the core, the difference in the outerdiameters along the core between the maximum outer diameter of the coreand the minimum outer diameter of the core is preferably not more than300×10⁻⁶ m, further preferably 200×10⁻⁶ m. When the difference in theouter diameters along the core exceeds 300×10⁻⁶ m, the core is notpreferable, because wrinkles and slacks are generated in the film rollby the effect of the core, even when the thickness unevenness of thepolyester film is small. The roll shape of the core is desirably a crownshape in which the central portion of the core in the width directionand both the end portions of the core are thick and thin, respectively.The crown shape facilitates the outward removal of air between the filmsand the inhibition of wrinkle generation, when the polyester film isrolled. In the core of the crown shape, the difference between thediameter of the central portion of the core and the diameters of boththe end portions of the core is preferably in the range of 0 m to300×10⁻⁶ m.

As a material for the above-described core, paper, a plastic or the likemay be used, but a fiber-reinforced plastic is preferably used from theviewpoint of strength. The core produced from the fiber-reinforcedplastic includes a core produced by winding around, for example, carbonfibers or glass filaments in a cylindrical shape, impregnating thecylindrical product with a thermosetting resin such as an unsaturatedpolyester resin and then curing the impregnation product.

The flexural modulus of the above-described core in the circumferentialdirection is preferably not less than 13 GPa, further preferably notless than 14 GPa. When the core having the flexural modulus notsatisfying the range is used, the core is often deformed by a tensionand a contact pressure generated when the polyester film is rolled. Amethod for adjusting the strength of the core within the range isespecially not limited, but the strength of, for example, a carbonfiber-reinforced plastic core can be adjusted by suitably selecting theamount of the carbon fibers, and a desired strength is further obtainedby adjusting the thickness of the core.

The surface roughness Ra of the above-described core is preferably notmore than 0.6 μm, further preferably not more than 0.3 μm. When a corenot satisfying the range is used, the surface roughness of the core istransferred to the surface of a polyester film. Thereby, when the coreis used for, for example, a film which is used for a high recordingdensity magnetic tape severely demanding the flatness of the film, theelectromagnetic transducing properties of the magnetic tape is sometimesremarkably deteriorated. A method for controlling the surface roughnessof the core within the range is especially not limited, but a desiredsurface roughness is obtained, for example, by disposing a resin layeron the surface of the core and then grinding the surface of the resinlayer in good accuracy.

The degree of surface hardness of the core is preferably not less than65 degree, further preferably not less than 70 degree. When a core notsatisfying the range is used, the core is often deformed by a tensionand a contact pressure generated on the rolling of the polyester film,and the deformation is often transferred to the film to produce adefective flat surface. A method for adjusting the degree of surfacehardness of the core within the range is especially not limited, but thedegree of surface hardness of the core can be adjusted by using a hardresin such as an epoxy resin on the surface of the core and thensuitably selecting the thickness.

The polyester film roll in the present invention is especially effectiveas a film roll for magnetic recording media which demand good flatness.The polyester film roll is effective as a polyester film roll fordigital recording method magnetic recording media among the magneticrecording media. Furthermore, among them, the polyester film roll in thepresent invention is effective as a polyester film roll, for magneticrecording media of ferromagnetic metal thin film layers, whose magneticlayer-formed side film surfaces demand the ultimate flatness, and whosenon-magnetic side film surfaces also demand flatness from the viewpointof thermal deterioration on vacuum deposition, besides maintaining of arolling-up property.

The degree of rolling hardness of the polyester film roll in the presentinvention is preferably adjusted to not less than 90 and not more than100 to prevent the generation of wrinkles with the passage of time andthe slippage of the rolled film as described above. In order to obtainthe roll having such the degree of hardness, the polyester film ispreferably rolled under conditions comprising a rolling tension of 5 to20 kg/m, a rolling contact pressure of 50 to 200 kg/m, a rolling speedof 20 to 200 m/minute, further preferably 40 to 200 m/minute. When thepolyester film roll is used as a magnetic recording medium, a coatinglayer for facilitating the adhesion or slipping of the polyester film isvery often disposed on the magnetic layer-forming side surface of thepolyester film. Therein, the polyester film is preferably rolled so thatthe magnetic layer-forming side surface of the film is arranged on theinner side to prevent the coating layer from being shaven with a contactpressure roll of a slitter.

Subsequently, the second polyester film roll of the present inventionwill be explained.

On the second polyester film, it should be understood that thedescriptions on the first polyester roll may be applied as such tomatters not described below.

The polyester film roll in the present invention is a polyester filmroll in which a polyester film is rolled on a core, and which, among thelengths of lines which are obtained by measuring the diameters of saidroll in the width direction of the roll, drawing a straight line betweenboth the ends of the curved line of the obtained roll diameters, andthen vertically drawing the lines from said curved line to said straightline, the maximum length (maximum convex portion) on the convex portionside from said straight line is not more than 500 μm, preferably notmore than 400 μm, especially preferably not more than 300 μm, and themaximum length (maximum concave portion) on the concave portion sidefrom said straight line is not more than 300 μm, preferably not morethan 200 μm, especially preferably not more than 150 μm.

When the maximum convex portion exceeds 500 μm, the film at the place isextended to cause problems such as the generation of Caterpillarrut-like wrinkles (slacks), the deterioration of the flatness, thefailure in the formation of an uniform coating film, the generation ofwrinkles to make it impossible to uniformly calender the film, when thefilm is calendered, and the generation of magnetic tapes having smallerwidths than a desired width, when slit into magnetic tapes. When themaximum concave portion exceeds 300 μm, air is accumulated at theportion in the width direction of the roll and causes problems such asthe formation of longitudinal wrinkles, when the air is removed, thefailure in the formation of an uniform coating film, and the failure ina uniform calendering operation, when the film is calendered.

The method for producing the above-described polyester film roll isespecially not limited, but preferably includes methods comprisingmeasuring the thickness of a continuously formed traveling film in highaccuracy, or using a die having a narrowed lip heater distance so as toenable the fine control in the thickness of the film, or properlysetting an oscillation width on a slitting operation, or adjusting thethickness of the film by measuring the roll shape values (diameters) ofthe rolled film roll in the width direction of the roll, and then byfeeding back the measured values to adjust the temperature and gap ofthe die lips so as to satisfy the roll shape of the present invention.The former highly accurate measuring method is the most ideal method,because the thickness of the film can be controlled in high response.But, the latter method can be combined with conventional thicknessunevenness-adjusting methods, and has advantages that the shortage inthe accuracy of the method can be covered and that an increase in thecost can be restrained. A non-contact method hardness meter, generallyused online, such as a transmitted β-ray attenuation method thicknessmeter, a transmitted infrared light attenuation method thickness meter,or an optical interferencial spectoscopy thickness meter, is used formeasuring the thickness of the traveling film by the former method. Anda stylus type thickness meter, a non-contact laser type thickness meter,or the like, is used for the latter roll shape method.

The width and length of the polyester film in the present invention areespecially not limited, but the width and the length are generally notless than 300 mm and not more than 1,500 mm, and not less than 3,000 mand not more than 30,000 m, respectively, from the viewpoint ofproductivity in an industrial scale. The effects of the presentinvention especially remarkably appear on the roll of a film having awidth of not less than 500 mm and a length of not less than 4,000 m.Also, the effects especially remarkably appear on the roll of a filmhaving a thickness of not less than 2 μm and not more than 10 μm,further preferably of not less than 3 μm and not more than 8 μm,especially preferably of not less than 4 μm and not more than 7 μm. Afilm having a thickness of less than 2 μm is difficult to be used as thesupport of a magnetic recording medium, because the rigidity of the filmis extremely lowered, while a film having a thickness of more than 10 μmis difficult to become the target of the present invention, because thefilm has a high rigidity and gives a relatively good rolled appearance.

The polyester film in the present invention exhibits the remarkableeffects, when at least one surface roughness Ra of the polyester film ispreferably not less than 0.1 nm and not more than 10 nm, furtherpreferably not less than 0.3 nm and not more than 8 nm, especiallypreferably not less than 1 nm and not more than 6 nm. The polyester filmhaving a surface roughness Ra of less than 0.1 nm is not preferable,because the polyester film has an inferior slipping property and givesonly film rolls having extremely inferior rolled appearances. On theother hand, a coarse polyester film having a Ra of more than 10 nmhardly becomes the target of the present invention, because thepolyester film scarcely generates wrinkles even when the shape of theroll does not satisfy the conditions of the present invention.

The outer diameter of the roll-shaped core of the polyester film roll inthe present invention is especially not limited, but is usually 80 to200 mm. And, it is preferable to use the core, wherein, among thelengths of lines which are obtained by measuring the diameters of thefilm-rolling portion of the core in the width direction of the core,drawing a straight line between both the ends of the curved line of theobtained core diameters, and then vertically drawling the lines fromsaid curved line to said straight line, the maximum length (maximumconvex portion) on the convex portion side from said straight line isnot more than 400 μm, preferably not more than 200 μm, especiallypreferably not more than 100 μm, and the maximum length (maximum concaveportion) on the concave portion side from said straight line is not morethan 200 μm, preferably not more than 100 μm, especially not more than50 μm. Even when the thickness unevenness of the polyester film islittle, the core in which the maximum convex portion exceeds 400 μm orin which the maximum concave portion exceeds 200 μm is not preferable,because longitudinal wrinkles and slacks are generated on the film rollby the effect of the core.

As described above, it should be understood that the descriptions on thefirst polyester film roll are applied as such to matters not describedherein on the second polyester film roll of the present invention.

(The Uses of the Polyester Film Roll)

In the present invention, as understood from the above-describedexplanations, the polyester films obtained from the first polyester filmroll and the second polyester film roll can advantageously be used assupports (base films) for magnetic recording media, capacitors,packages, printing materials, and so on, especially as supports for highdensity magnetic recording media (video tapes, audio tapes, computertapes, and so on).

EXAMPLES

Hereinafter, the present invention will further be explained withexamples, but the present invention is not limited to thebelow-described examples, so long as not exceeding the essential pointsof the present invention. And, the characteristic values were measuredby the following methods.

Polyethylene terephthalate of raw material is melted and extruded in afilmy shape by the use of an extruder, cooled, oriented in the machinedirection at a draw ratio of 3 to 6, and then oriented in the transversedirection at a draw ratio of 3 to 6. Between the machine-directionorienting process and the transversely orienting process a coatingliquid may be coated on the side of the film to dispose a coating layer.The film may further be reoriented in the machine direction and in thetransverse direction. The film is then thermally set to form thepolyester film having a thickness in a range of 0.5 to 20 μm, preferablyin a range of 2 to 10 μm, which is rolled, for example, as a jumbo roll.Therein, as described above, the thickness of the traveling film isaccurately measured by an online measuring method, or the roll shapevalues of the rolled film roll in the width direction are measured. Themeasured values are fed back for the adjustment of the temperature andgap of die lips so as to satisfy the roll shape of the presentinvention, thus adjusting the thickness of the film. The film is slitinto films having prescribed widths and lengths by the use of a slitter.When the film is slit, the jumbo roll may be oscillated to disperse thethickness unevenness in the width direction. By the oscillation, rollshape defects due to small thickness unevenness can be reduced. When thefilm is slit, the obtained films are adhered to cores with a paste,adhesive tapes, or a liquid such as water or an alcohol. The obtainedfilms are rolled in a prescribed length, while a desired rolling tensionand a desired rolling contact pressure are applied to the films with theslitter.

(1). The Surface Roughness Ra of the Film

According to JISB 0601, the center line average roughness of the film isdetermined with a stylus type surface roughness meter (surfcoderSE30FAT) manufactured by (Ltd.) Kosaka Kenkyusho under conditionscomprising a stylus tip radius of 2 μm, a measuring pressure of 30 mg, acutoff of 0.08 mm and a measuring length of 1.25 mm. The measurementsare carried out four times, and the average value is used as the surfaceroughness Ra of the film.

(2). The Shapes of the Polyester Film Roll and the Core in the WidthDirection

(2-1). The Case of the First Polyester Film Roll

The roll shape of the film roll is measured with a bulk shape measurermanufactured by Kitano Kikaku (Ltd.) in the width direction, and adifference between the maximum outer diameter of the roll and theminimum outer diameter of the roll is determined from the measureddiameters. The maximum and minimum outer diameters of the roll aredetermined by measuring diameters of the roll at three positions at adistance of 120 degree in the circumferential direction and then themeasured diameters are averaged. The measured data in the ranges of boththe ends of the film roll to 0.010 m positions are deleted to remove theeffects of the high edges of the film end surfaces.

(2-2). The Case of the Second Polyester Film Roll

The roll shape of the film roll is measured with a bulk shape measurermanufactured by Kitano Kikaku (Ltd.) in the width direction, and acurved line showing the change of the diameters is determined. Eachdiameter is determined by measuring diameters at three positions at adistance of 120 degree in the circumferential direction and then themeasured values are averaged. Both the ends of the curved line are boundto each other to form a straight line. Lines are vertically drawn fromconvex portions to the obtained straight lines, and the maximum convexportion is determined. Lines are also vertically drawn from concaveportions to the straight line, and the maximum concave portion isdetermined. The measured data in the ranges of both the ends of the filmroll to 0.01 m positions are deleted to remove the effects of the highedges of the film end surfaces.

The film-rolling portion of the core on which the film is rolled is alsomeasured as described above, and the maximum convex portion and themaximum concave portion are determined.

(3). The Degree of Surface Hardness of the Polyester Film Roll

A hardness tester, type C, manufactured by Kobunshi Keiki (Ltd.) ispressed on the polyester film roll to measure the degree of surfacehardness. Measuring points are totally 15 measuring points which consistof three measuring points at a distance of 120 degree in thecircumferential direction at each of five points in the width directionof the polyester film roll (wherein the width obtained by removing boththe 0.010 m long end widths from the overall width of the roll isdivided into five equal portions, and the measurements are carried outat the three measuring positions in the center of each of the equalportions).

(4). The Flexural Modulus of the Core in the Circumferential Direction

The flexural modulus is determined by measuring the deflection of aring-like test piece (width: 50 mm) with a universal tester, when a loadis applied to the test piece in the circumferential direction, and thensubstituting the measured value into the following equation.Eγ=0.149Pr ³/(δI)*10⁻³,

wherein,

-   -   cross-sectional secondary moment I=50t³/12    -   Eγ; elastic modulus (GPa) in the circumferential direction    -   P; load (N)    -   r; central diameter (mm)    -   δ; deflection (mm)    -   t; core thickness (mm).        (5). The Degree of Surface Roughness Rac of the Core

According to JIS B0601, the degree of surface roughness Rac of the coreis determined by measuring a degree of central line average roughness atthe center of the core in the width direction and at two positions apartfrom both the ends at distances of 0.050 m with cutoffs of 0.25 mm,respectively, by the use of Surfcom 111 A, a surface roughness meter ofTokyo Seimitsu (Ltd.) and then averaging the measured values.

(6). The Degree of Surface Hardness of the Core

According to the JIS K7215, the degree of surface hardness of the coreis determined by pressing a hardness tester, type D manufactured byKobunshi Keiki (Ltd.) on the center of the core in the width directionand on places apart from both the ends of the core at distances of 0.050m, respectively, to measure the degrees of surface hardness at the threepositions and then averaging the measured values.

(7). Young's Modulus

The Young's modulus is determined by cutting off a test piece having awidth of 10 mm and a length of 150 mm from the film, pulling the testpiece at a distance of 100 mm between the chucks of an instron typeuniversal tensile tester at a pulling rate of 10 mm/minute and at achart rate of 500 mm/minute and then calculating the Young's modulusfrom the tangential line at the standing-up portion of the obtainedload-elongation curve.

Comparative Example 1

The pellets of polyethylene 2,6-naphthalenedicarboxylate substantiallynot containing inactive particles were dried at 170° C. for 6 hours, fedinto an extruder and then melted at 305° C. The melted polymer wasfiltered by a known method, extruded from the extruder into a sheet-likeproduct, and then quenched and solidified on a casting drum to producethe non-oriented film. Subsequently, the non-oriented film waspreliminarily heated at 120° C., machine-direction oriented between alow speed roll and a high speed roll at an orientation ratio of 3.7under a 900° C. IR heater disposed at a height of 15 mm above the film,and then coated with aqueous solutions having the followingcompositions, respectively.

The Side of the Surface A

-   -   a copolyester (terephthalic acid/isophthalic acid/5-sodium        sulfoisophthalic acid/ethyleneglycol/bisphenol A·two        propyleneoxide adduct=97/1/2/60/40): 80 parts.    -   acrylic particles (average particle diameter: 30 nm): 5 parts.    -   SS-70 produced by Sanyo Kasei: 15 parts.    -   thickness (after dried): 5 nm.        The Side of the Surface B    -   a copolyester (terephthalic acid/isophthalic acid/5-sodium        sulfoisophthalic acid/ethyleneglycol/bisphenol A·two        propyleneoxide adduct=97/1/2/60/40): 60 parts.    -   acrylic particles (average particle diameter: 40 nm): 10 parts.    -   hydroxyethylmethylcellulose: 20 parts.    -   Nonion NS-208.5 produced by Nippon Yushi: 10 parts.    -   thickness (after dried): 20 nm.

Subsequently, the film was fed into a stenter, oriented at a orientationratio of 4.9 in the transverse direction at 150° C., further oriented ata ratio of 1.14 in the transverse direction at 200° C. andsimultaneously thermally treated to obtain the biaxially oriented filmhaving a thickness of 4.7 μm, which is rolled as a jumbo roll. Theobtained biaxially oriented film has a Ra of 0.7 nm on the surface A and3.3 nm on the surface B. The thickness of the biaxially oriented filmwas measured by the online scanning of a transmitted β-ray attenuationmethod thickness meter in the width direction, and the measurementresults were fed back to the temperatures of the die lips to control thethickness of the film. The jumbo roll was rerolled on a fiber-reinforcedplastic (FWP) core into a film roll having a width of 0.500 m, a lengthof 9,000 m and a rolling hardness of 99 degree under conditionscomprising a rolling tension of 10 kg/m, a rolling contact pressure of140 kg/m, a rolling rate of 100 m/minute, an oscillation width of 0.100m, and an oscillation rate of 0.010 m/minute. The fiber-reinforcedplastic (FWP) core had a length of 0.550 m, a crown-like shape, adifference of 120×10⁻⁶ m between the maximum diameter and the minimumdiameter in the width direction, a flexural modulus of 15.7 GPa in thecircumferential direction, a degree of surface roughness of 0.2 μm and adegree of surface hardness of 85 degree. The shape of the film roll inthe width direction was measured with a bulk shape measurer manufacturedby Kitano Kikaku (Ltd.). But, the shape of the roll did not satisfy thespecifications of the present invention, and wrinkles were generated onthe roll.

Example 1

A jumbo roll of a biaxially oriented film having a thickness of 4.7 μmwas produced and then slit by the same method as in the comparativeexample 1 except that the roll shape of the obtained film roll wasmeasured and then fed back for the adjustment of the temperatures of dielips and for the adjustment of the gap between the lips to reduce thethickness unevenness of the film. The shape of the obtained film roll inthe width direction was measured. It was consequently found that thefilm roll had the roll shape satisfying the conditions of the presentinvention, and wrinkles were not recognized on the roll not only justafter slit but also after the passage of 24 hours.

Comparative Example 2

On the production of the film in the comparative example 1, the film ofthe jumbo roll was rerolled on a fiber-reinforced plastic (FWP) core toform a film roll having a width of 0.620 m, a length of 7,000 m and adegree of rolling hardness of 98 degree under conditions comprising arolling tension of 10 kg/m, a rolling contact pressure of 100 kg/m, arolling rate of 100 m/minute, an oscillation width of 0.100 m, and anoscillation rate of 0.010 m/minute. The fiber-reinforced plastic (FWP)core had a length of 0.67 m, a crown-like shape, a difference of150×10⁻⁶ m between the maximum diameter and the minimum diameter in thewidth direction, a flexural strength of 15.7 GPa in the circumferentialdirection, a degree of surface roughness of 0.2 μm and a degree ofsurface hardness of 85 degree. The shape of the film roll in the widthdirection was measured with a bulk shape measurer manufactured by KitanoKikaku (Ltd.). But, the shape of the roll did not satisfy thespecifications of the present invention, and wrinkles were generated onthe roll.

Example 2

A jumbo roll of a biaxially oriented film having a thickness of 4.7 μmwas obtained and then slit by the same method as in the comparativeexample 2 except that the roll shape of the obtained film roll wasmeasured and then fed back for the adjustment of the temperature of thedie lips and for the adjustment of the gap between the die lips toflatten the unevenness of the roll shape and simultaneously reduce thethickness unevenness of the film. The shape of the obtained film roll inthe width direction was measured. It was consequently found that thefilm roll had the roll shape satisfying the conditions of the presentinvention, and wrinkles were not recognized on the roll not only justafter slit but also after the passage of 24 hours.

Comparative Example 3

On the production of the polyester film in the comparative example 1,the polyethylene 2,6-naphthalenedicarboxylate was changed intopolyethylene terephthalate, and the polyethylene terephthalate wasprocessed similarly except the following conditions to obtain a 6.4 μmthick biaxially oriented film. The conditions comprise a pellet dryingtime of 3 hours, a melting extrusion temperature of 295° C., amachine-direction orienting pre-heating temperature of 80° C., alongitudinal orientation ratio of 3.0, coating only the surface A withthe same coating liquid as that coated on the surface A in thecomparative example 1, transversely orienting the film at a orientationratio of 3.3 at 105° C., further transversely orienting the film at aorientation ratio of 1.6 at 210° C., and simultaneously thermallytreating the film. The Ra of the obtained biaxially oriented film was0.7 nm on the surface A and 3.0 nm on the surface B. A film roll wasproduced under the same slitting condition as in the comparativeexample 1. But, the shape of the roll did not satisfy the conditions ofthe present invention, and wrinkles are generated on the roll.

Example 3

A jumbo roll of a 6.4 μm-thick biaxially oriented film was obtained andthen slit by the same method as in the comparative example 3 exceptoperations comprising measuring the shape of the obtained film roll,feeding back the measurement results to the temperature of the die lipsand to the gap between the die lips to flatten the unevenness of theroll shape, and simultaneously controlling the thickness of the film.The shape of the obtained film roll in the width direction was measured.It was consequently found that the film roll had the roll shapesatisfying the conditions of the present invention, and wrinkles werenot recognized on the roll not only just after slit but also after thepassage of 24 hours.

Comparative Example 4

On the production of the polyester film in the comparative example 1, a4.7 μm-thick biaxially oriented polyester film was obtained by the samemethod as in the comparative example 1 except operations comprisingchanging the extrusion of polyethylene 2,6-naphthalenedicarboxylatesubstantially not containing inactive particles to the coextrusion of araw material A comprising polyethylene 2, 6-naphthalenedicarboxylatesubstantially not containing inactive particles and a raw material Bcomprising polyethylene 2,6-naphthalenedicarboxylate substantially notcontaining inactive particles and containing 0.3 wt. % of silicaparticles having an average particle diameter of 300 nm in a thicknessratio of 3:2, and changing coating the surfaces A and B with the coatingliquids to coating only the surface A with the same coating liquid asthat coated on the surface A in the comparative example 1. The Ra of theobtained film was 1.3 nm on the surface A and 5.8 nm on the surface B. Afilm roll was produced under the same slitting condition as in thecomparative example 1. But, the shape of the film roll did not satisfythe conditions of the present invention. The rolled appearance of thefilm roll was good just after slit, but wrinkles were generated on theroll after the passage of 24 hours.

Example 4

A jumbo roll of a 4.7 μm-thick biaxially oriented film was obtained andthen slit by the same method as in the comparative example 4 exceptoperations comprising measuring the roll shape of the obtained filmroll, feeding back the measurement results to the temperatures of dielips and to the gap between the die lips to flatten the unevenness ofthe roll shape, and simultaneously controlling the thickness of thefilm. The shape of the obtained film roll in the width direction wasmeasured. It was consequently found that the film roll had the rollshape satisfying the conditions of the present invention, and wrinkleswere not recognized on the roll not only just after slit but also afterthe passage of 24 hours.

TABLE 1 The Rolled Appearance of the Roll Roll At the W L 2W × 10⁻³ L ×10⁻⁷ R Just after Passage of 24 [m] [m] [10⁻⁶m] [10⁻⁶m] [10⁻⁶m] Slithours after Slit Example 1 0.500 9,000 1,000 900 300 Very good Very goodExample 2 0.620 7,000 1,240 700 220 Very good Very good Example 3 0.5009,000 1,000 900 250 Very good Very good Example 4 0.500 9,000 1,000 900350 Very good Very good Comparative 0.500 9,000 1,000 900 1,200 Bad BadExample 1 Comparative 0.620 7,000 1,240 700 810 Bad Bad Example 2Comparative 0.500 7,000 1,000 700 950 Bad Bad Example 3 Comparative0.500 9,000 1,000 900 1,030 Good Bad Example 4

These results are shown in Table 1.

As apparent from Table 1, the polyester film roll of the presentinvention did not have wrinkles generated thereon, and had a good rolledappearance.

Comparative Example 5

The pellets of polyethylene 2,6-naphthalenedicarboxylate containing 0.02percent by weight of calcium carbonate having an average particlediameter of 0.6 μm and 0.3 percent by weight of spherical silicaparticles having an average particle diameter of 0.1 μm were dried at170° C. for 6 hours, fed into an extruder and then melted at 305° C. Themelted polymer was filtered by a known method, extruded from a diehaving a lip gap of 60 mm, and then quenched and solidified on a castingdrum to obtain the unoriented film. The unoriented film waspreliminarily heated at 120° C., further heated with a 900° C. IR(infrared light) heater disposed at a 15 mm-high place, oriented at aratio of 4.7 in the machine direction between a low speed roll and ahigh speed roll, fed into a stenter, oriented at a ratio of 5.0 in thetransverse direction at 150° C., and then thermally treated at 200° C.to obtain the 6.0 μm-thick biaxially oriented film, which was rolled asa jumbo roll. The obtained biaxially oriented film had a Ra of 8 nm, aYoung's modulus of 6.9 GPa in the machine direction and a Young'smodulus of 7.2 GPa in the transverse direction. The thickness of thebiaxially oriented film was measured by the online scanning of atransmitted β-ray attenuation method thickness meter in the widthdirection, and the measurement results were fed back to the temperaturesof the die lips to control the thickness of the film. The film of thejumbo roll was rerolled on a fiber-reinforced plastic (FWP) core througha slitter under conditions comprising a rolling tension of 10 kg/m, arolling contact pressure of 140 kg/m, a rolling rate of 100 m/minute, anoscillation width of 100 mm, and an oscillation rate of 0.010 m/minuteto obtain the film roll having a width of 1.0 m, a length of 5,000 m anda degree of rolling hardness of 99 degree. The fiber-reinforced plastic(FWP) core had a length of 1.2 m, the maximum convex portion of 100 μmand the maximum concave portion of 100 μm in the width direction, aflexural strength of 15.7 GPa in the circumferential direction, a degreeof surface roughness of 0.2 μm and a degree of surface hardness of 85degree. The shape of the film roll in the width direction was measuredwith a bulk shape measurer manufactured by Kitano Kikaku (Ltd.), and astraight line was drawn between both the ends of the curved line of themeasured diameters. Lines were vertically drawn from convex portions tothe straight line, and among the lengths of the lines, the length of themaximum convex portion was 700 μm. Lines were also vertically drawn fromconcave portions to the straight line, and among the lengths of thelines, the length of the maximum concave portion was 400 μm. After thepassage of 24 hours, the film was pulled out from the film roll, and theflatness of the film was examined. Consequently, the generation ofCaterpillar rut-like wrinkles (slackened wrinkles) was recognized at themaximum convex portion, and the generation of longitudinal wrinkles wasalso found out at the maximum concave portion. Thus, the film was bad inthe flatness, and had the problem in practical use.

Example 5

A jumbo roll of a biaxially oriented film was obtained and then slit togive a film roll by the same method as in the comparative example 5′except the employment of a die having a lip gap of 30 mm (the lip gap ofthe die was a half of that in the comparative example 5). The shape ofthe obtained film roll in the width direction was measured with a bulkshape measurer manufactured by Kitano Kikaku (Ltd.) by a similar methodas in the comparative example 5. Among the lengths of lines which wereobtained by measuring the shape of the film roll in the width direction,drawing a straight line between both the ends of the obtained curvedline, and then vertically drawing the lines from the convex portions tothe straight line, the length of the maximum convex portion was 450 μm,and among the lengths of lines which were similarly obtained byvertically drawing the lines from the concave portions to the straightline, the length of the maximum concave portion was 250 μm. After thepassage of 24 hours, the film was pulled out from the film roll, and theflatness of the film was examined. Consequently, the generation ofCaterpillar rut-like wrinkles (slackened wrinkles) was slightlyrecognized at the maximum convex portion, and the generation oflongitudinal wrinkles was also slightly found out at the maximum concaveportion. However, the Caterpillar rut-like wrinkles and the longitudinalwrinkles disappeared, when the film was lightly pulled. Thereby, theCaterpillar rut-like wrinkles and the longitudinal wrinkles did notcause a trouble in practical use.

Example 6

A jumbo roll of a biaxially oriented film was obtained and then slit togive a film roll by the same method as in the comparative example 5except that the oscillation width was changed to 150 mm (lipgap×transverse orientation ratio). The shape of the obtained film rollin the width direction was measured with a bulk shape measurermanufactured by Kitano Kikaku (Ltd.) by the same method as in thecomparative example 5. Among the lengths of lines which were obtained bymeasuring the shape of the film roll in the width direction, drawing astraight line between both the ends of the obtained curved line, andthen vertically drawing the lines from the convex portions to thestraight line, the length of the maximum convex portion was 250 μm, andamong the lengths of lines which were similarly obtained by verticallydrawing the lines from the concave portions to the straight line, thelength of the maximum concave portion was 150 μm. After the passage of24 hours, the film was pulled out from the film roll, and the flatnessof the film was examined. Consequently, the generation of Caterpillarrut-like wrinkles (slackened wrinkles) was not recognized at the maximumconvex portion, and the generation of longitudinal wrinkles was also notfound out at the maximum concave portion. Thereby, the flatness of thefilm was very good.

Example 7

A jumbo roll of a biaxially oriented film was obtained by the samemethod as in the example 6. The shape of the obtained film roll in thewidth direction was measured with a bulk shape measurer manufactured byKitano Kikaku (Ltd.), and die lip heaters corresponding to the positionsof the convex portions and concave portions of the obtained curved lineof the roll shape were adjusted together with the online automaticcontrol of a transmitted β-ray attenuation method thickness meter. Thejumbo roll obtained thus was slit to give a film roll by the same methodas in the example 6. The shape of the obtained film roll in the widthdirection was measured with the bulk shape measurer manufactured byKitano Kikaku (Ltd.) by the same method as in the example 6. Among thelengths of lines which were obtained by drawing a straight line betweenboth the ends of the obtained curved line and then vertically drawingthe lines from the convex portions to the straight line, the length ofthe maximum convex portion was 200 μm, and among the lengths of lineswhich were similarly obtained by vertically drawing the lines from theconcave portions to the straight line, the length of the maximum concaveportion was 100 μm. After the passage of 24 hours, the film was pulledout from the film roll, and the flatness of the film was examined.Consequently, the generation of Caterpillar rut-like wrinkles (slackenedwrinkles) was not recognized at the maximum convex portion, and thegeneration of longitudinal wrinkles was also not found out at themaximum concave portion. Thereby, the flatness of the film was verygood.

Example 8

The pellets of polyethylene terephthalate containing 0.25 percent byweight of spherical silica particles having an average particle diameterof 0.1 μm and used for a layer A, and the pellets of polyethyleneterephthalate containing 0.05 percent by weight of cross-linked siliconeresin particles having an average particle diameter of 0.6 μm and 0.4percent by weight of alumina particles having an average particle(secondary particle) diameter of 0.1 μm and used for a layer B weredried at 170° C. for 3 hours, fed into two extruder hoppers,respectively, melted at 300° C., and then extruded from a multi-manifoldtype coextruder die having a lip gap of 30 mm to obtain the sheet-likelaminate where the layer A is laminated to one side of the layer B in aratio of 7:3. The extruded sheet-like laminate was quenched andsolidified on a casting drum to obtain the non-oriented film. Thenon-oriented film was preliminarily heated at 75° C., further heatedwith a 830° C. IR (infrared light) heater from a 14 mm-high place andsimultaneously oriented at a ratio of 2.3 in the machine directionbetween a low speed roll and a high speed roll, quenched, fed into astenter, oriented at a ratio of 3.6 in the transverse direction at 110°C., preliminarily heated at 110° C., oriented at a ratio of 2.5 betweena low speed roll and a high speed roll, further fed into a stenter, andthen thermally set at 210° C. for 10 seconds to obtain the 6.0 μm-thickbiaxially oriented film, which was rolled as a jumbo roll. The biaxiallyoriented film had a surface roughness Ra of 4 nm on the surface A, asurface roughness Ra of 8 nm on the surface B, a Young's modulus of 7.8GPa in the machine direction, and a Young's modulus of 4.7 GPa in thetransverse direction. The shape of the obtained jumbo roll in the widthdirection was measured with the bulk shape measurer manufactured byKitano Kikaku (Ltd.), and die lip heaters corresponding to the positionsof the convex portions and concave portions of the obtained curved lineof the roll shape were adjusted together with the online automaticcontrol of a transmitted β-ray attenuation method thickness meter. Thejumbo roll obtained thus was slit by the same method as in the example 7except that the oscillation width was changed to 110 mm, therebyobtaining a film roll. The shape of the obtained film roll in the widthdirection was measured with the bulk shape measurer manufactured byKitano Kikaku (Ltd.) by the same method as in the example 7. Among thelengths of lines which were obtained by drawing a straight line betweenboth the ends of the obtained curved line and then vertically drawingthe lines from the convex portions to the straight line, the length ofthe maximum convex portion was 150 μm, and among the lengths of lineswhich were similarly obtained by vertically drawing the lines from theconcave portions to the straight line, the length of the maximum concaveportion was 100 μm. After the passage of 24 hours, the film was pulledout from the film roll, and the flatness of the film was examined.Consequently, the generation of Caterpillar rut-like wrinkles (slackenedwrinkles) was not recognized at the maximum convex portion, and thegeneration of longitudinal wrinkles was also not found out at themaximum concave portion. Thereby, the flatness of the film was verygood.

Comparative Example 6

A jumbo roll of a biaxially oriented film was obtained, and then slit togive a film roll by the same method as in the comparative example 5except that the oscillation ratio was changed to 150 mm. The shape ofthe obtained film roll in the width direction was measured with a bulkshape measurer manufactured by Kitano Kikaku (Ltd.) by the same methodas in the comparative example 5. Among the lengths of lines which wereobtained by drawing a straight line between both the ends of theobtained curved line, and then vertically drawing the lines from theconvex portions to the straight line, the length of the maximum convexportion was 550 μm, and among the lengths of lines which were alsosimilarly obtained by vertically drawing the lines from the concaveportions to the straight line, the length of the maximum concave portionwas 250 μm. After the passage of 24 hours, the film was pulled out fromthe film roll, and the flatness of the film was examined. Consequently,the generation of longitudinal wrinkles was slightly found out at themaximum concave portion. When the film was lightly pulled, the finelongitudinal wrinkles disappeared, and did not cause a trouble. However,the generation of Caterpillar rut-like wrinkles (slackened wrinkles)were recognized at the maximum convex portion to deteriorate theflatness of the film, and caused troubles in practical use.

Comparative Example 7

A jumbo roll of a biaxially oriented film was obtained by the samemethod as in the comparative example 5. The shape of the obtained jumboroll in the width direction was measured with a bulk shape measurermanufactured by Kitano Kikaku (Ltd.), and die lip heaters correspondingto the positions of the convex portions and concave portions of theobtained curved line of the roll shape were adjusted together with theonline automatic control of a transmitted β-ray attenuation methodthickness meter. The jumbo roll obtained thus was slit to give a filmroll by the same method as in the comparative example 5. The shape ofthe obtained film roll in the width direction was measured with the bulkshape measurer manufactured by Kitano Kikaku (Ltd.) by the same methodas in the comparative example 5. Among the lengths of lines which wereobtained by drawing a straight line between both the ends of theobtained curved line and then vertically drawing the lines from theconvex portions to the straight line, the length of the maximum convexportion was 300 μm, and among the lengths of lines which were similarlyobtained by vertically drawing the lines from the concave portions tothe straight line, the length of the maximum concave portion was 350 μm.After the passage of 24 hours, the film was pulled out from the filmroll, and the flatness of the film was examined. Consequently, thegeneration of Caterpillar rut-like wrinkles (slackened wrinkles) werenot recognized at the maximum convex portion, but the generation oflongitudinal wrinkles were found out at the maximum concave portion todeteriorate the flatness of the film was bad, and caused troubles inpractical use.

These results are shown in the table 2. As apparent from the table 2,the polyester film roll of the present invention was free from thegeneration of wrinkles, had a good rolled appearance, and did not causea trouble in practical use.

TABLE 2 Unit E. 5 E. 6 E. 7 E. 8 C.E. 5 C.E. 6 C.E. 7 Polymer PEN PENPEN PET PEN PEN PEN Layer Single Single Single Two Single Single SingleConstitution Layer Layer Layer Layers Layer Layer Layer SurfaceRoughness Layer A [nm] 7 7 7 4 7 7 7 Layer B [nm] 7 7 7 9 7 7 7 TotalRatio # 1 [Ratio] 4.7 4.7 4.7 5.75 4.7 4.7 4.7 # 2 [Ratio] 5.0 5.0 5.03.6 5.0 5.0 5.0 # 3 [nm] 30 30 30 30 60 60 60 # 4 [nm] 100 150 150 108100 150 100 Roll Size Film [mm] 1,000 1,000 1,000 1,000 1,000 1,0001,000 Width Film [m] 5,000 5,000 5,000 5,000 5,000 5,000 5,000 LengthRoll Shape # 5 [μm] 450 250 200 150 700 550 300 # 6 [μm] 250 150 100 100400 250 350 Rolled Appearance of the Film Roll #7 Good Very Very VeryBad Bad Good Good Good Good #8 Good Very Very Very Bad Good Bad GoodGood Good E.: Example C.E.: Comparative Example # 1: Ratio in theMachine Direction # 2: Ratio in the Transverse Direction # 3: Die LipHeater Distance # 4: Oscillation Width # 5: Maximum Convex Portion # 6:Maximum Concave Portion # 7: Longitudinal Wrinkles # 8: SlackenedWrinkles

According to the present invention, a polyester film roll, which doesnot generate wrinkles and slacks with the passage of time, gives narrowslit film-products having accurate widths, and has a good rolledappearance even with flat surfaces, can be provided, without theproblems that the characteristics of a film must be changed as acountermeasure for a good rolled shape of a film roll, and that thecharacteristics of a film is also changed to improve the conventionaltechnical problems, such as, wrinkles and slacks are generated with thepassage of time, even if they are not found during rolling of the film;the width of the slit film for a magnetic tape is partially narrowedafter being slit from a wide film; and the development of thetechnologies for rolling a flat thin film is extremely difficult, sothat they are not applied for commercial production. Thereby, theindustrial value of the present invention is high.

The invention claimed is:
 1. A polyester film roll comprising: a roll ofpolyester film, said polyester film being rolled onto a core, whereinsaid core has a maximum outer diameter and a minimum outer diameter, thedifference between said maximum and minimum outer diameters of the corebeing not more than 300×10⁻⁶ m.
 2. The polyester film roll described inclaim 1, wherein said maximum and minimum outer diameters of the coreare along the width direction of the core.
 3. The polyester film rolldescribed in claim 1, wherein said maximum outer diameter of the core isat a central portion of the core.
 4. The polyester film roll describedin claim 3, wherein said minimum outer diameter of the core is at an endportion of the core.
 5. The polyester film roll described in claim 1,wherein the flexural modulus of said core in the circumferentialdirection is not less than 13 Gpa.
 6. The polyester film roll describedin claim 1, wherein the surface roughness of said core is not more than0.6 μm.
 7. The polyester film roll described in claim 1, wherein thedegree of surface hardness of the core is not less than 65 degree. 8.The polyester film roll described in claim 1, wherein the degree ofrolling hardness of said roll is 90 to
 100. 9. The polyester film rolldescribed in claim 1, wherein the difference between a maximum outerdiameter of the roll and a minimum outer diameter of the roll is notmore than 2W×10⁻³ and not more than L×10⁻⁷, “W” being the width of theroll and “L” being the rolled length of the polyester film.
 10. Thepolyester film roll described in claim 9, wherein said maximum andminimum outer diameters of the roll are along the width direction of theroll.
 11. The polyester film roll described in claim 9, wherein saidrolled length of said polyester film is not less than 4,000 m.
 12. Thepolyester film roll described in claim 9, wherein said width of the rollis not less than 300 mm.
 13. The polyester film roll described in claim1, wherein the surface roughness of said polyester film is 1 to 10 nm.14. The polyester film roll described in claim 1, wherein the thicknessof said polyester film is 2 to 10 nm.
 15. The polyester film rolldescribed in claim 1, wherein said polyester film contains inactiveparticles.
 16. The polyester film roll described in claim 15, whereinsaid inactive particles is from the group consisting of calciumcarbonate particles, alumina particles, spherical silica particles, andtitanium oxide particles, and organic particles represented bycross-linked silicone resin particles, cross-linked polystyrene resinparticles, cross-linked acrylic resin particles, cross-linked polyesterresin particles, cross-linked styrene-acrylic resin particles, polyimideparticles, melamine resin particles.
 17. The polyester film rolldescribed in claim 15, wherein said inactive particles an averageparticle diameter of said inactive particles is not less than 0.01 μmand not more than 2.0 μm.
 18. The polyester film roll described in claim15, wherein a content of said inactive particles is not less than notless than 0.001 percent by weight and not more than 2.0 percent byweight.
 19. The polyester film roll described in claim 1, wherein saidpolyester film supports a magnetic recording medium.
 20. The polyesterfilm roll described in claim 19, wherein a coating layer is between saidpolyester film and said magnetic recording medium.
 21. The polyesterfilm roll described in claim 19, wherein said magnetic recording mediumis a ferromagnetic metal thin film layer.
 22. The polyester film rolldescribed in claim 19, wherein said magnetic recording medium is adigital recording method magnetic recording medium.
 23. The polyesterfilm roll described in claim 1, wherein a plurality of diameters of saidroll along the width direction of the roll is represented by a curvedline having ends, a straight line connecting said ends of the curvedline, wherein a maximum length from a maximum convex portion of saidcurved line to said straight line is not more than 500 μm.
 24. Thepolyester film roll described in claim 23, wherein a maximum length froma maximum concave portion of said curved line to said straight line isnot more than 300 μm.